The present invention is directed generally to a medical pump for feeding a fluid to a living body and/or pumping or discharging the fluid therefrom and more particularly, though not intended for a limit to this, to an artificial heart, serving as a substitute for a vital heart or as an auxiliary to the vital heart, for circulating blood in vivo.
Whether the operation of, e.g., an artificial heart is correct or not is of much significance in a medical sense. The artificial heart has a rated range of a stroke width in terms of structure. If driven in excess of this range, the artificial heart will undergo serious damages in structure, which probably gives a remarkable hazard to the living body to which the artificial heart is connected. The hazardous situation is derived from an excessive expansion of the discharge passage on one hand and an excessive collapse on the other hand.
The overexpansion causes the discharge to impinge and rub on a casing, with the result that it will be worn away due to a long stretch of use and presumably eventually ruptured. Whereas in the case of the overcollapse, an overload is applied on a driving module for driving the artificial heart, and the driving module is thereby damaged electrically or mechanically. The overcollapse also presents a high probability that erythrocytes will be destroyed in addition to abrasion caused by rubbing the inner surfaces against each other. Hence, a system for monitoring operational conditions thereof is required. It is a common practice that an image of a reversible operating body of the artificial heart is displayed on a monitor TV by incorporating a small-sized video camera like a CCD camera into the artificial heart. In order to help monitoring only by visual observation, a monitoring system disclosed in Japanese Patent Application No. 62839/1987 is constituted such that movement of the blood is photographed by means of a CCD camera in time series to accumulate the images thereof which are then partly extracted, and these images are arranged in a direction of a time axis to exhibit variations with a passage of time. In this type of monitoring system also, the correctness or incorrectness of the operation and an availability or unavailability of increase in blood flow rate have to be judged by visually confirming the images. It is therefore difficult to make a judgment from the images formed by photographing the operating body. Besides, a misjudgment tends to be made.
In the above-described monitoring system, the operator likewise has to judge an adequateness or inadequateness of the blood flow rate through his visual recognition of the images. The judgment from the images of the operating body is effected with difficulty.
Parts of the artificial heart, which are brought into contact with the blood, undergo an antithrombotic treatment to prevent thrombus. The blood flows at an adequate velocity under normal using conditions, and there is caused no blood stagnation in contact portions of a blood pump with the blood, thereby producing no thrombus. It is because blood platelets are not activated. However, if a flow rate of the blood from the artificial heart is extremely small; or a stroke per heartbeat is small; or an interval between one heartbeat and the next heartbeat is too long even when the stroke suffices, the blood becomes stagnant locally, and a time for which the blood stops in some parts of the discharge passage of the artificial heart. This phenomenon increases the probabilities that the platelets tend to be activated in those portions to facilitate the generation of thrombus, and the activated platelets spread over respective parts of the living body to clog peripheral blood vessels. For this reason, there are set a minimum flow rate under which the amount of flowing blood should not decrease, a least stroke and a maximum pulsation interval in the artificial heart.
If the passage for removing the blood from the living body and ejecting it therethrough is abnormally deformed, a blood pumping flow rate fluctuates. In addition, a local stagnation of the blood is produced in the suck, where the platelets are activated to cause the thrombus at a high probability. Simultaneously, stress locally acts on the suck, resulting in a breakage after a long period of time. Where the passage abnormally deflects, similar problems arise. The artificial heart continues to be employed for a relatively long period of time, and hence the above-mentioned system for monitoring the artificial heart is needed. The monitoring system is capable of judging an abnormal deformation, an abnormal deflection and a rupture of the suck by visually recognizing time-series configurational variations in the passage image. In this monitoring system also, the operator is required to judge the correctness or incorrectness of the suck operation through his visual recognition of the images. It is similarly difficult to make a judgment from the images obtained by photographing the operating body. A misjudgment is likely to be made.
An arrangement of a monitoring system disclosed in Japanese Patent Laid-Open Publication No. 158864/1985 is that a passage thickness is measured by making use of a Hall element preparatory to conversion into a passage volume, and a flow rate of blood is calculated from variations in the volume which are based on time-series changes in passage thickness.
According to the monitoring system disclosed in Japanese Patent Laid-Open Publication No. 158864/1985, a flow rate of the blood ejected by the artificial heart is automatically measured without relying on the judgment by visual observation of the operator, and it follows that the operator does not have to presume the flow rate of the ejected blood. The flow rate of the ejected blood, however, depends on conditions of the living body to which the artificial heart is connected as well as on a driving cycle and a driving pressure of the artificial heart. In other words, there are cases where the blood flow rate increases but does not rise particularly when intensifying a drive of the artificial heart. Hence, even if the flow rate of the ejected blood is automatically calculated by measuring the suck thickness in time series, the operator is unable to know whether the flow rate of the ejected blood should be increased or reduced.
According to the foregoing monitoring system, a flow rate of the blood ejected from the artificial heart is automatically measured without relying on the judgment by visual observation of the operator, whereby the operator does not have to presume the flow rate of the ejected blood. The properness or unproperness thereof can be determined from the blood flow rate. However, even when the artificial heart ejects the blood whose amount is greater than a minimum flow rate at which, for example, the platelets are not virtually activated, and if the passage biases on an expanding or contracting side in consequence of its stroke deviating from a normal range, an operating state of the passage varies, and the blood is apt to stagnate partially in the passage. Based on the method of measuring the flow rate by means of the monitoring system disclosed in Japanese Patent Laid-Open Publication No. 158864/1985, it is impossible to detect or judge an abnormality in such an operating state.
In the above-mentioned monitoring system, the overexpansion or overcollapse of the passage can not automatically be detected. Therefore, the operator has hitherto monitored directly the artificial heart or indirectly through a monitor camera by the visual observation. To be specific, the operator judges the overexpansion or overcollapse in an intellectual manner by visually recognizing a configuration of the pulsating passage. Such a monitoring operation, however, requires a good deal of labor, because the operation has to continue during a period for which the artificial heart works, as a result of which a judgment error or a monitoring mistake is likely to take place.
In the monitoring system described above, if the Hall element is equipped apart from the passage, the measurement by the Hall element becomes inaccurate, because variations in the passage thickness are small. This in turn makes a measurement value of the flow rate inaccurate. When mounting the Hall element on the passage, relatively precise measurement may be attained. It is, however, considerably difficult to mount the Hall element on the passage. Besides, there arise problems in which expanding/contacting characteristics of the passage change, and the excessive stress is applied locally on the passage, resulting in a decline of its durability.
In the aforementioned monitoring system, it is unfeasible to directly monitor an abnormal deformation, an abnormal deflection and a rupture of the passage. It is a large burden on the operator to monitor directly the artificial heart all the time or indirectly via a monitor TV, and at the same time there is a high probability that a misjudgment or monitoring mistake is to be caused.